Automatic tuning circuit



y 1.953 I A. BUCKSBAUM 2,645,719

AUTOMATIC TUNING CIRCUIT Filed Sept. 16, 1950 j (z TCOWOL TGIWD TERM/N4LZ9 lllll ll PLATE SCREEN GRID TERMINAL R1 cfg j REFERE/Jcf uvvzmoa ARuow M. EMA sown fv z a a: Mom? F Q v BY 74 i x a 1 Patented July 14, 195 3 UNITED STATES PATENTVOFFICE Arnold M. Bucksbaum,

This invention relates to automatic tuning devices.

It is an object of this invention to provide an automatic tuning circuit that will stabilize frequencies.

Another object of this invention is to provide automatic tuning means for a resonant cavity which forms the plate load of an ultra-high frequency tube.

A feature of this invention is found in the provision for a tunable cavity that form the plate load of an ultra-high frequency tube and which is excited by the tube at a particular frequency. A pair of loops extend into the cavity and pick up opposite phase voltages to compare them with a reference voltage. A direct current output proportional to the off-resonant voltage is obtained from the comparison circuit.

Further objects, features and advantages of this invention will become apparent from the description and claims when read in view of the drawings, in which:

Figure 1 is a schematic view of the automatic tuner of this invention, and,

Figure 2 is a vector diagram of the reference voltages at the resonant condition.

Figure 1 illustrates a coaxial cavity member, designated generally as Ill, which has a center portion II that extends axially of the cavity and a plunger [2 which is disc: shaped and formed with a central opening to pass over the member H. A bracket I3 is connected to the disc [2 and is threadedly received on a lead screw M which is .rotatably mounted to one end of the cavity member I0. Rotation of the lead screw [4 causes the bracket 13 to move axially of the cavity In and thus move the washer l2 back and forth in the cavity. A driving means l6, which may be a direct current motor for example, is connected to the lead screw 14 to impart rotary motion thereto.

The end wall I! of the cavity is grounded and has mounted therein an ultra-high frequency tube I8 which might be, for example, an Eimac type 4X150A. The control grid contact H! of the tube extend through the wall I! and is insulated therefrom. The screen grid 2| is coupled to the wall I1 through the bypass condensers 22. The plate 23 of the tube is received within the center post I l and is insulated therefrom by insulation 24. A lead 26 which contains a radio frequency choke 21 connects the plate to B+.

An input circuit 28 is coupled to a tuned circuit 29 which is connected between the grid [9 Cedar Rapids, Iowa, assignor to Collins Radio Company, Cedar Rapids, Iowa, a corporation of Iowa Application September 16, 1950, Serial No. 185,278

2 Claims. (01. 250-40) and the resistor R1 and condenser C1. The opposite sides of the condenserand resistor are connected to ground. The resistor R1 provides the grid bias for the tube l8, and the capacitor C1 is a radio frequency bypass-condenser. A capacitor C2 is connected to the grid IS. A pair of pickup loop-s 33 and 34 extends into the resonant are connected to R2 and R3, respectively, and a pair of condensers C3 and C4 are connected between the outputs of the diode rectifiers 36 and 31 and have the mid-point thereof grounded. A pair of resistors R6 and R7 are also connected 7 across the outputs of the rectifiers 36 and 31 and have their mid-point grounded.

Leads 33 and 39 are connected to the resistors R6 and R7 and furnish an input to a direct current amplifier Al. The amplifier 4| furnishes an input to the direct current motor 16 which in turn controls the tuning of the cavity by moving the plunger l2.

The values of the components might be, for example:

C1-500 micromicrofarads. C11 micromicrofarad. C3500 micromicrofarads. C4-500 micromicrofarads. R1-22,000 ohms.

R3-47 ohms.

R4100 ohms.

R5100 ohms.

The manner in which the tuner functions is that the input supplied by 28, which might be for example, 450 megacycles, is impressed on the grid I9 through the tuned circuit 29. The condenser C2 is a degree phase shifter. The loops 33 and 34 pick up voltages which are degrees out of phase and add them through the resistors R2, R3, R4 and R5 to the reference voltage from condenser C2. When the inductance of the cavity in combination with the output capacity of the tube are resonant at the input frequency, the vector diagram of Figure 2 will appropriate and the voltages from loops 33 and 34 will form a right angle with the reference voltage. This is true because When the disc I2 is adjusted to the resonant position the pickup voltages and the grid voltage will be in phase, and out of phase, respectively. The voltages picked up by the loops 33 and 34 will be 90 and 270 with respect to the reference voltage. When the cavity is not at the resonant condition, the reference voltage will not be 90 and 270 degrees out of phase with the voltages picked-up, and therefore the angle a, shown in Figure 2, will be greater than or less than 90 degrees depending upon whether the cavity is above or below resonance. E1 and E2 will not be equal at this condition and thus an output will be obtained from the direct current amplifier 4|. The polarity of this output will give the correct sense to the motor so that it runs in the desired direction to reestablish the resonant condition.

The output of loop 33 is added to the reference voltage from condenser C2 and their sum is supplied to the rectifier 35. Likewise, the voltage from loop 34 is added to the reference voltage from the condenser C2 and their sum is supplied to the diode 37. Since the rectifiers 36 and 31' pass current in only one direction, if meter 42 which has a zero-center needle is connected across the outputs of the diodes 36 and 3?, it will read zero for the resonant condition. When resonance does not exist the outputs of rectifiers 35 and 3? will not be equal and the difference will be amplified and drive the motor [5.

Another novel feature of this invention is that if the input signal supplied to 28 is frequency modulated, the modulation will appear between leads 38 and 39. This is true because a frequency modulated signal varies about the carrier and if the cavity is tuned to the carrier frequency, the modulation excursions will be detected.

Thus it is seen that this invention provides means for automatically tuning a resonant cavity.

Although this invention has been described with respect to a particular embodiment thereof, it is not to be so limited as changes and modifications may be made therein which are within the full intended scope of the invention as defined by the appended claims.

I claim: l

1. Means for automatically maintaining a cavity resonator at resonance comprising, tuning means movable longitudinally of said cavity resonator, drivin means connected to said tuning means, a first and second loop mounted closely adjacent to each other and oriented 180 degrees with respect to each other so as to pick up voltages of opposite phase, an electronic valve mounted within said cavity, a driving signal supplied to the grid of said electronic valve, a degree phase-shifter connected to said grid, signal adding means receiving the output of said phase shifter to add it separately to the outputs of the first and second loops, voltage comparing means receiving the outputs of said adding means to give an output proportional to the difference between the incoming signals, and the output of said comparing means supplied to the driving means. i

2. Means for tuning a cavity resonator having a slidable tuning member comprising, driving means connected to said tuning means, an ultrahigh frequency electronic valve mounted in said resonator, an exciting signal supplied to the grid of said electronic valve, a 90 degree phase-shifter receiving a signal from said grid, first and second pickup loops mounted closely adjacent each other within said cavity to pick up voltages that are degrees apart, first and second resistors connected in series across the first and second pickup loops, the output of said phase shifter connected between said first and second resistors, first and second rectifying means connected, respectively, to "the outputs of said first and second pick-up loops and subtracting means receiving the output of said rectifiers and giving an output proportional to the difference therein and supplying said output to said driving means.

ARNOLD M. BUCKSBAUM.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,304,377 Roberts Dec. 8, 1942 2,412,482 Vilkomerson Dec. 10, 1946 2,462,857 Ginzton et a1 Mar. 1, 1949 2,464,818 Learned Mar. 22, 1949 

